HOME    MEMS Sensor    Smart Sensor    Environmental Monitoring    NDIR CO2 Carbon Dioxide Sensor

NDIR CO2 Carbon Dioxide Sensor

PN:RK0801
  • RK080X series infrared gas sensor. Used in indoor air quality testing, HVAC systems, fresh air equipment, air purification equipment, fans, automatic window control, etc., with good selectivity and stability. It is widely used all over the world.

    For the design and manufacture of RK080x series infrared ground sensors, this manual provides important design technical suggestions. Please read this manual carefully before use.

      

    1. Overview

    This manual covers our infrared gas sensor RK0801 and RK0802. The design accuracy and size of these models are different. Table 1 summarizes the basic similarities and differences of these models.

    RK080x series infrared sensors are designed and manufactured based on Lambert-Beer's law, used to detect target gases, and belong to physical sensors. Not affected by material consumption, the life span is generally longer than that of chemical sensors.

    Table 1: Comparison of module models

    Model

    RK0801

    RK0802

    size

    39.6x 17 x 9(mm)

    33 x 17 x 9 (mm)

    Design accuracy

    ±(50ppm+5% reading value)

    ±(50ppm+5% reading value)

     

    1. Technical parameters
      1. Technical parameters

    Table 2: RK080x technical parameters

    Model

    RK0801

    RK0802

    measurement range

    4002000ppm (0-1%VOL optional)

    working principle

    Non-dispersive infrared (NDIR)

    Operating Voltage

    4.55.5V DC

    4.55.5V DC

    Working current

    120mA peak

    20mA average

    120mA peak

    20mA average

    Precision

    ±(50ppm+5% reading value)

    ±(50ppm+5% reading value)

    Preheat time

    3min

    3min

    Response time

    T90 <120s

    T90 <120s

    Detection interval

    2s

    2s

    Working conditions

    050/090%RH (no condensation)

    Storage conditions

    -2060/090%RH (non-condensing)

    Communication Interface

    UART level 3.3V

    PMW

      1. Interface definition
      2. Table 3.  RK080x interface definition

    Pin

    name

    Features

    PIN1PIN8

    CAL

    Clean air zero point adjustment input

    PIN2PIN9PIN12

    NC

    No connection

    PIN3PIN15

    GND

    Ground potential

    PIN4PIN16

    VDD

    Supply voltage

    PIN5PIN11

    RXD

    UART (RXD) data input

    PIN6PIN10

    TXD

    UART (TXD) data output

    PIN7PIN13

    PWM

    Pulse width modulation

     

     

     

    1. Power supply impact

    In order to ensure the normal operation of the sensor, the operating voltage of the sensor is kept in the range of 4.0V~5.5V DC. Exceeding this voltage range may cause malfunction or the sensor cannot work normally.

    In order to ensure the normal operation of the sensor, the current output capacity of the power supply should not be less than 150mA. If the power supply current capacity is lower than this value, it may cause a malfunction or the sensor cannot work normally.

     

    4. Interface design

    RK080x infrared gas sensor provides multiple output interfaces such as UART and PWM, which can be individually calibrated. It is very convenient to connect the product with the user.

    4.1 UART interface

    The UART interface is the interface with the most complete functions of this sensor. It is recommended that users use the UART interface. The user-end equipment can read the gas concentration value directly through the sensor's UART interface.(The user terminal needs to use TTL level, if it is RS232 level, please perform level conversion first).The VDD-GND-RXD-TXD of the sensor is connected to the user's 5V-GND-TXD-RXD respectively.

    4.1.1 Communication interface settings

    If the user uses the UART interface, set the UART communication mode according to the following table.

     

     

     

    Table 4. UART settings

    Baud rate

    9600

    Data bit

    8-bit

    Stop bit

    1 bit

    Parity bit

    no

     

    4.1.2 Communication commands

    Table 5. Communication command list

    Protocol command interface list and meaning

    0x86

    Read gas concentration value

    0x87

    Calibration zero (ZERO)

    0x88

    Calibration span point (SPAN)

    0x79

    Turn on/off the automatic zero calibration function

       

    0x86-Read gas concentration value

    send command

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    Reserved

    command

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x01

    0x86

    0x00

    0x00

    0x00

    0x00

    0x00

    0x79

    return value

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    command

    8 bits higher in concentration

    Concentration lower 8 bits

    -

    -

    -

    -

    Check value

    0xFF

    0x86

    HIGH

    LOW

    -

    -

    -

    -

    Checksum

    Gas concentration value = HIGH * 256 + LOW

     

     

     

    0x79-open/close automatic zero calibration

    send command

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    Reserved

    command

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x01

    0x79

    0xA0/0x00

    0x00

    0x00

    0x00

    0x00

    Checksum

    return value

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    command

    status

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x79

    0x01/0x00

    -

    -

    -

    -

    -

    Checksum

     

    Note: When Byte3 in the sending command is 0xA0, the automatic calibration function is turned on; when Byte3 is 0x00, the automatic calibration function is turned off. The sensor factory default is to turn on the automatic zero calibration function.

    In the return value, Byte2 is the status, 0x01 indicates that the modification is successful, and 0x00 indicates that the modification fails.

     

     

    0x87-Zero point calibration command

    send command

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    Reserved

    command

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x01

    0x87

    0x00

    0x00

    0x00

    0x00

    0x00

    Check value

    return value

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    command

    status

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x87

    0x01/0x00

    -

    -

    -

    -

    -

    Checksum

     

    Note: Byte2 in the return value is the status, 0x01 indicates that the calibration is successful, and 0x00 indicates that the calibration has failed.

    The zero point refers to 400ppm. Before sending the zero point calibration command, please make sure that the sensor runs stably at a concentration of 400ppm for more than 20 minutes.

     

     

     

     

    0x88-Calibrate SPAN point command

    send command

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    Reserved

    command

    SPAN high 8 bits

    SPAN lower 8 bits

    -

    -

    -

    Check value

    0xFF

    0x01

    0x88

    HIGH

    LOW

    0x00

    0x00

    0x00

    Checksum

    return value

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    command

    status

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x88

    0x01/0x00

    -

    -

    -

    -

    -

    Checksum

     

    Example: If the SPAN value is 2000ppm, then HIGH = 2000/256; LOW = 2000% 256

    Note: Byte2 in the return value is the status, 0x01 indicates that the calibration is successful, and 0x00 indicates that the calibration has failed.

    Please calibrate the zero point before calibrating the SPAN value.

    Before sending the SPAN calibration command, please ensure that the sensor runs stably for more than 20 minutes at the corresponding concentration.

    It is recommended to use 2000ppm as the SPAN value for calibration. If you need to use a lower value as the span value, please choose a value above 1000ppm.

     

    4.1.3 Checksum

    In order to enhance the reliability of sensor communication, a checksum setting is added to the communication protocol. If the checksum fails, communication is not possible. The specific checksum calculation method is as follows:

    Checksum = (Invert (Byte1+Byte2+Byte3+Byte4+Byte5+Byte6+Byte7))+1.

    example:

    Byte0

    Byte1

    Byte2

    Byte3

    Byte4

    Byte5

    Byte6

    Byte7

    Byte8

    Start byte

    Reserved

    command

    -

    -

    -

    -

    -

    Check value

    0xFF

    0x01

    0x86

    0x00

    0x00

    0x00

    0x00

    0x00

    Checksum

    The calculation is as follows:

    1. Add from Byte1 to Byte7: 0x01 + 0x86 + 0x00 + 0x00 + 0x00 + 0x00 + 0x00 = 0x87
    2. Invert: 0xFF-0x87 = 0x78
    3. Add 1 after inversion: 0x78 + 0x01 = 0x79

     

    C language checksum calculation routine:

    C language calculation checksum routine

    char getCheckSum(char *packet)

    {

    char i, checksum;

    for( i = 1; i< 8; i++)

    {

    checksum += packet[i];

    }

    checksum = 0xff – checksum;

    checksum += 1;

        return checksum;

    }

    4.2 PWM interface

    RK080x series sensors provide PWM interface, which uses pulse width to characterize target gas concentration. Take a sensor with a measurement range of 2000ppm as an example:

     

    CO2 concentration output range

    02000ppm

    cycle

    1004ms±5%

    High level output at the beginning of the cycle

    2ms (theoretical value)

    Middle cycle

    1000ms±5%

    Low level output at the end of the period

    2ms (theoretical value)

    The formula for obtaining the current CO2 concentration value through PWM: Cppm=2000×(TH-2ms)/(TH+TL-4ms)

    Cppm is the CO2 concentration value obtained by calculation, the unit is ppm

    TH is the time when the output is high in an output cycle

    TL is the time when the output is low in one output cycle

     

     

    5.Calibration

    RK080x series sensors have two calibration methods: zero point calibration and SPAN point calibration.

    5.1 Zero point calibration

    In order to facilitate the user to calibrate the zero point, RK080x series sensors have three zero calibration methods: manual zero calibration, command zero calibration and automatic zero calibration. The zero point calibration function refers to calibrating 400ppm.

    5.1.1 Manual zero point calibration

    Manual zero point calibration is to input a low level (0V) to the CAL pin of the sensor to calibrate the zero point. The low level needs to last for more than 7 seconds. Before calibrating the zero point, make sure that the sensor runs stably for more than 20 minutes at a concentration of 400ppm.

    5.1.2 Automatic zero point calibration

     The automatic calibration function means that the sensor will intelligently judge the zero point according to the environmental concentration and calibrate itself after a period of continuous operation. The calibration cycle is automatically calibrated once every 26 hours since power-on and operation. The zero point for automatic calibration is 400 ppm.

     The automatic zero calibration function is suitable for office environment and home environment. But it is not suitable for agricultural greenhouses, breeding farms, cold storage and other places. In such places, the automatic zero calibration function should be turned off. After closing, the user is required to perform zero point detection on the sensor regularly, and if necessary, command zero calibration or manual zero calibration.

    5.1.3 Command zero calibration

    Sending calibration commands to the sensor through the serial port (UART) can realize the zero point calibration of the sensor. For the zero point calibration command, please refer to the 0x87-zero point calibration command in the communication.

    5.2 SPAN point calibration

    Send a calibration command to the sensor through the serial port (UART) to realize the SPAN point calibration of the sensor. For SPAN point calibration command, please refer to 0x88-Calibrate SPAN point command in communication.

    1. Printed circuit board and shell design
      1. The influence of the position of the sensor

    Infrared sensors are physical sensors and only reflect light inside. Normally, the installation position of the sensor has no effect on the measurement.

      1. Temperature sensor

    The infrared sensor is temperature sensitive. In order to accurately measure the ambient temperature around the sensor, the location of the temperature sensor should be as close as possible to the sensor.

      1. Sensor housing design

    In order to make the measurement response speed fast enough, the air-permeable part of the sensor housing should be designed to be permeable, and the sensor should be close to the housing opening. It is recommended to use a design with openings on both sides of the housing to improve air flow.

    1. Packaging design

    Infrared sensors are physical sensors that detect gas concentration by light intensity. The physical shape of the sensor may be affected by vibration and pressure during the calculation process, and the sensor measurement may be affected and deviate from the original calibration range. Therefore, it is possible to make shock absorption design in packaging design. Such as adding pearl sponge or foam to the packaging to absorb shock.